1. Field of the Invention
The present invention relates to a probe with a switchover device for a measuring instrument, in particular, an oscilloscope.
2. Related Technology
Voltage probes for oscilloscopes are available in a range of variants. Active probes are used primarily for high-frequency signals beyond 1 GHz; whereas passive waveguide probes provide a cost-favourable alternative. In the case of passive-waveguide probes, the measuring tip is connected directly to the waveguide, which is terminated with 50Ω, so that the circuit to be measured is loaded on the basis of the low impedance of 50Ω.
A high-voltage probe, which provides a high-frequency coaxial cable, which is closed by its surge impedance over the majority of the high-frequency range, is known from DE 41 40 506 A1. Moreover, the high-voltage probe described in DE 41 40 506 A1 comprises a circuit with resistors and capacitors, which provide a fixed division ratio independently of the input frequency. The exemplary embodiments described in DE 41 40 506 A1 l cover an overall measurement range from 0 Hz (direct current) to more than 100 MHz (high-frequency), this range being subdivided into four individual measurement ranges, so that each exemplary embodiment covers a given frequency range. The disadvantage in this context is that, when measuring a frequency range, which extends from direct current (0 Hz) up to high-frequency alternating currents of more than 100 MHz, the high-voltage probe must be changed several times. Furthermore, it is disadvantageous that the high-voltage probes described in DE 41 40 506 A1 are designed to measure voltages within the range of several tens of thousands of volts because of the high-voltage balancing ratio. A connected voltage of approximately 1 volt would no longer be registered with adequate precision by these high-voltage probes.